Coiled filter strip with upstream and downstream butt ends

ABSTRACT

A filter element comprising at least one coiled filter strip defining first and second butt ends, one of the butt ends being arranged to define an upstream surface during normal filtering operation, receiving fluid to be filtered, and the other of the butt ends being arranged to define a downstream surface during normal filtering operation, through which filtered fluid leaves the coiled strip.

This is a continuation of application Ser. No. 07/567,638 filed Aug. 15,1990, now U.S. Pat. No. 5,174,895, itself a continuation of applicationSer. No. 07/297,496 filed Jan. 17, 1989, now U.S. Pat. No. 5,015,379.

FIELD OF THE INVENTION

The present invention relates to fluid filter apparatus generally andmore particularly to backflushable filters for liquids, such as water.

BACKGROUND OF THE INVENTION

Various types of backflushable filters are known. A particularly usefultype of such filters is the disk filter, which is comprised of a stackof filter disks. Disk filters are described and claimed in applicant'sU.S. Pat. No. 4,683,060.

SUMMARY OF THE INVENTION

The present invention seeks to provide a new type of backflushablefilter which is highly efficient, easy to clean, and relativelyinexpensive to manufacture, and which provides, in a small physicalarea, a large filter surface area.

There is thus provided in accordance with a preferred embodiment of thepresent invention a filter element comprising at least one coiled filterstrip defining first and second butt ends, one of the butt ends beingarranged to define an upstream surface during normal filteringoperation, receiving fluid to be filtered, and the other of the buttends being arranged to define a downstream surface during normalfiltering operation, through which filtered fluid leaves the coiledstrip.

Additionally in accordance with an embodiment of the invention thefilter strip is formed to have one surface defining an array oflongitudinally extending filter grooves extending along the longitudinalaxis of the filter strip and to have an opposite surface defining aspacer groove which engages filter grooves, when the filter strip iscoiled, to define a filtration pathway of predetermined cross sectionand collection regions for particles which do not pass through thefiltration pathway.

According to an alternative embodiment of the invention, the filterelement is formed of at least two filter strips coiled together.Preferably, the at least two filter strips comprise a filtering stripand a spacer strip. The filtering strip may comprise a grooved strip or,preferably a porous strip.

Additionally in accordance with an embodiment of the present invention,the coiled filter strip or strips are held closely together by beingcoiled. Alternatively, the coil or the strips may be held in a tightcondition by the use of adhesive or by welding, such as ultrasonicwelding.

According to one embodiment of the invention, the coiled filter strip orstrips may be coiled about a hollow tube.

Further in accordance with a preferred embodiment of the presentinvention, there is provided a backflushable filter comprising at leastone filter element of the type described above and apparatus forsupplying fluid to be filtered to a first end of the filter elementdefining an upstream filter element surface and for receiving filteredfluid from the opposite end thereof defining a downstream filter elementsurface.

Additionally in accordance with an embodiment of the invention, there isalso provided means for supplying backflushing fluid to the downstreamfilter element surface and means for removing the fluid received fromthe upstream filter element surface.

Further in accordance with an embodiment of the invention, the means forremoving includes means for vacuum scanning of the upstream filterelement surface.

Still further in accordance with an embodiment of the present invention,there is provided a technique for manufacture of filter elementscomprising the steps of extruding at least one filter strip, embossingthe at least one filter strip with a groove pattern, and coiling the atleast one filter strip.

Further in accordance with this embodiment of the invention, there isalso provided the step of extruding over the coiled filter a cylindricalcover.

Additionally in accordance with an embodiment of the invention,following the step of extruding the cover, end caps, defining fluidinlets or outlets are fitted in sealing engagement over the coiledfilter.

Further in accordance with an embodiment of the invention, there is alsoprovided a step of securing the coiled filter strip in tight engagementwhich comprises the step of bonding, which may be achieved by means ofadhesive or welding, such as ultrasonic welding.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood and appreciated more fully fromthe following detailed description taken in conjunction with thedrawings in which:

FIG. 1 illustrates a single filter strip in partially coiledorientation;

FIG. 1B shows a sectional illustration of the single filter strip ofFIG. 1 in coiled orientation;

FIG. 2 illustrates a pair of filter strips in partially coiledorientation in accordance with one embodiment of the invention;

FIG. 2B illustrates a pair of filter strips in partially coiledorientation according to an alternative embodiment of the presentinvention;

FIG. 2C shows a sectional illustration of the pair of filter strips ofFIG. 2 taken along lines C--C, in coiled orientation;

FIG. 3 illustrates a pair of filter strips in partially coiledorientation in accordance with another embodiment of the invention;

FIG. 3B shows a sectional illustration of the pair of filter strips ofFIG. 3 in coiled orientation;

FIG. 4 illustrates a technique for producing a coiled filter strip ofthe type shown in FIG. 1;

FIG. 5 illustrates a technique for producing coiled filter strips of thetype shown in FIG. 2;

FIGS. 6A and 6B illustrate a technique for producing coiled filterstrips of the type shown in FIG. 3;

FIG. 7 illustrates a technique for producing coiled filter stripsaccording to an alternative embodiment of the present invention;

FIG. 7B shows a sectional illustration of the coiled filter stripsproduced by the technique of FIG. 7;

FIG. 8 illustrates an extrusion technique for enclosing coiled filterstrips;

FIGS. 9A, 9B and 9C, illustrate three alternative embodiments of coiled,enclosed filter strips;

FIG. 10 is a side view interior illustration of a backflushable filterconstructed and operative in accordance with a preferred embodiment ofthe present invention and employing filter elements formed of coiledfilter strips;

FIG. 11 is a sectional illustration taken along the lines XI--XI of FIG.10;

FIG. 12 is a pictorial illustration of a detail of the backflushingapparatus taken along the lines XII--XII of FIG. 10;

FIGS. 13 and 14 are side view interior illustrations of two alternativetypes of filters employing a filter element formed of a coiled filterstrip having a central flowthrough passage formed therein.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Reference is now made to FIG. 1, which illustrates a partially unwoundfilter element 10 formed of a coiled filter strip 12. In this embodimentof the invention, the filter strip 12 comprises a relatively thin stripof material, typically a flexible plastic having two different patternsformed thereon. On a first surface 14 there is typically provided arelatively smooth background surface 16 from which protrudes a spacergroove defining protrusion 18, typically in the form of a generallysinusoidal, undulating wave, which extends generally back and forthbetween first and second edges 20 and 22 of the surface.

Spacer groove defining protrusion 18 is preferably but not necessarilyof uniform thickness and may be of any desired thickness, depending onthe size of the particles to be filtered.

On a second, opposite surface 24 of strip 12, there is formed an array26 of filter grooves, which extend generally transversely with respectto spacer groove defining protrusion 18, except at the points ofinflection thereof, adjacent the first and second edges 20 and 22. Thefilter grooves of array 26 are sized so as to provide precisely definedfiltration down to particles of a given minimum size.

Filter groove array 26 is typically bordered adjacent both edges 20 and22 by non-grooved raised portions 28 and 30 respectively, whichcorrespond in thickness to the height of the peaks of the intersticesbetween the grooves of array 26.

It will be appreciated that a complete filter element employing a coiledfilter strip of the type illustrated in FIG. 1, will have upstream anddownstream filter surfaces for inlet of a fluid such as water to befiltered and exit thereof, respectively, at either of its butt ends 32and 34, defined respectively by edges 20 and 22. The filter strip 12illustrated in FIG. 1 is symmetrical with respect to edges 20 and 22 andthus it does not matter which butt end is coupled as the upstream filtersurface. Alternatively, the filter strip 12 may be modified in one of awide variety of ways to render it non-symmetric.

One possible modification would be to make the spacer grooves defined byprotrusion 18 and facing edge 20 of larger area than those spacergrooves facing edge 22. Other modifications are also possible.

It is noted that when filter element 10 is ready for use, it is tightlywound together and may, if desired, be bonded together by any suitabletechnique, such as adhesive bonding or ultrasonic welding, such that theouter facing edge of protrusion 18 sealingly engages borders 28 and 30where they are in facing relationship and also sealingly engages thepeaks of the interstices between the grooves of array 26. A sectionalillustration of this engagement is provided in FIG. 1B.

Assuming, for the purposes of discussion that the upstream end of thefilter element 10 is at end 32, it is appreciated that fluid, such aswater to be filtered, enters the filter at end 32 and passes throughdirt accumulation grooves 36 which are defined by protrusion 18 andcommunicate with the upstream end 32 and then passes through thecross-sectional areas of the filter grooves of array 26, past thejuxtaposed portion of facing protrusion 18, as illustrated in FIG. 1B.The thus filtered fluid, then passes through exit grooves 37 as it exitsvia downstream end 34.

Reference is now made to FIG. 2 which illustrates an alternativeembodiment of filter element 10, which is comprised of two filter strips42 and 44 coiled together. Filter strip 42 is typically formed of aporous material, such as polyester cartridge or polypropylene cartridgeor any desired type of mesh and defines first and second edges 48 and50. For the purposes of description herein, it is assumed that edge 48is located at the upstream end of the element 40, and that edge 50 islocated at the downstream end of the element. It is specifically notedthat the filter strip 42 may be formed of porous material of any desiredcharacteristics and pass through specifications and that the term,"porous material" as used herein, also includes screen material of anysuitable mesh size. It also includes single or multiple layer porousmaterial with uniform or different pass through characteristics.

Filter strip 44 typically defines a spacer strip having spacer groovepatterns formed on opposite surfaces 52 and 54 thereof and respectiveedges 58 and 60. On surface 52, there is defined a groove patterndefining debris collecting grooves 56 communicating with edge 58, whileon surface 54 there are defined generally back-to-back with grooves 56,exit grooves 62, communicating with edge 60.

Grooves 56 are defined by raised portions 64 which include a raisedborder 65 adjacent edge 60, while grooves 62 are defined by raisedportions 66, which include a raised border 67 adjacent edge 58.

In order to provide maximum structural strength to spacer strip 44, theraised portions 64 and 66 can be somewhat skewed with respect to eachother as illustrated in FIG. 2B, such that raised portion 64 willdiagonally overlie raised portion 66. This arrangement enables theplanar portion of surfaces 52 and 54 to be made very thin.

It is noted that when filter element 40 is ready for use, it is tightlywound together and may, if desired, be bonded together by any suitabletechnique, such as adhesive bonding or ultrasonic welding, such that theinner facing edge 68 of porous filter strip 42 sealingly engages raisedportions 64 and border 65 of spacer strip 44 to define debris collectionchambers. Similarly, it is preferred but not essential, that outerfacing surface 69 of porous filter strip 42 sealingly engage raisedportions 66 and border 67 of spacer strip 44. A sectional illustrationof this engagement is provided in FIG. 2C.

Reference is now made to FIG. 3 which illustrates yet anotherconfiguration of filter element constructed and operative in accordancewith a preferred embodiment of the present invention and which hassimilarities to both of the embodiments described hereinabove. Theembodiment of FIG. 3 comprises two filter strips 70 and 72 which arecoiled together to define a filter element 74.

Filter strip 70 is typically formed with identical first and second sidesurfaces 76 and 78, each of which is formed with a generallylongitudinally extending groove array 80, which may be similar in allrelevant respects to groove array 26 described in connection with theembodiment of FIG. 1, hereinabove, and which is bordered alongrespective first and second edges 82 and 84 by raised border portions 86and 88 respectively.

Filter strip 72 is typically formed with identical first and second sidesurfaces 90 and 92, each of which is formed with a relatively smoothbackground surface 96 from which protrudes a spacer groove definingprotrusion 98, typically in the form of a generally sinusoidal,undulating wave, which extends generally back and forth between firstand second edges 100 and 102 of the surface.

Spacer groove defining protrusions 98 are preferably but not necessarilyof uniform thickness and may be of any desired thickness depending onthe size of the particles to be filtered.

It will be appreciated that a complete filter element employing a coiledfilter strip of the type illustrated in FIG. 3, will have upstream anddownstream filter surfaces for inlet of a fluid such as water to befiltered and exit thereof, respectively, at either of its butt ends 130and 132.

The filter element 74 is symmetrical with respect to ends 130 and 132and thus it does not matter which butt end is coupled as the upstreamfilter surface. Alternatively, the filter strip 72 may be modified inone of a wide variety of ways to render it non-symmetric.

One possible modification would be to make the spacer grooves defined byprotrusion 98 and facing edge 100 of larger area than those spacergrooves facing edge 102. Other modifications are also possible.

When filter element 74 is ready for use, it is tightly wound togetherand may, if desired, be bonded together by any suitable technique, suchas adhesive bonding or ultrasonic welding, such that the outer facingedge of protrusion 98 sealingly engages borders 86 and 88 where they arein facing relationship and also sealingly engages the peaks of theinterstices between the grooves of array 80. A sectional illustration ofthis engagement is provided in FIG. 3B.

Assuming, for the purposes of discussion, that the upstream end of thefilter element 74 is at end 132, it is appreciated that fluid, such aswater to be filtered, enters the filter at end 132 and passes throughdirt accumulation grooves 136 which are defined by protrusion 98 andcommunicate with the upstream end 132 and then pass through thecross-sectional areas of the filter grooves of array 80, past thejuxtaposed portion of facing protrusion 98, as illustrated in FIG. 3B.The thus filtered fluid, then passes through exit grooves 137 as itexits via downstream end 130.

Reference is now made to FIG. 4 which illustrates apparatus forproducing a filter strip of the type illustrated in FIG. 1. A stripextruder 150, receives a supply of a thermoplastic material such aspolyethylene or polypropylene or any similar desired material andproduces a strip of such material. While the strip is still hot andformable, it passes between a pair of embossing rollers 152 and 154,which respectively form thereon the patterns formed on respectivesurfaces 24 and 14 of strip 12 (FIG. 1). The strip is then coiled toform the filter element 10. If coiled while still in a plastic state,simple tight coiling may be sufficient to hold the coil sufficientlytightly together such that it is effectively heat welded withoutrequiring any additional heat welding step.

FIG. 5 illustrates the corresponding production of the filter element ofFIG. 2, it being noted that the porous strip 42 is not embossed but thespacer strip 44 is embossed on both sides by rollers 156 and 158 withthe respective patterns which appear on surfaces 52 and 54 thereof. Theextrusion apparatus 160 may be identical to that employed in theembodiment shown in FIG. 4.

FIG. 6 illustrates the production of the filter element of FIG. 3. Thestrip 70 is produced by an extruder 170 and embossing rollers 172 and173, while the strip 72 is produced by an extruder 174 and embossingrollers 176 and 178. The two embossed strips are then rolled together todefine filter element 74.

FIG. 7 illustrates an alternative embodiment of the invention, wherein afirst filter strip 180 having formed thereon an embossed pattern of,possibly but not necessarily skewed, spacer protrusions 182 of the typetypically illustrated in FIG. 1, and having formed on the spacerprotrusions transverse filter grooves 184, is heat welded byconventional welding rollers 186 and 188 to a smooth strip 190 thusproducing a filter strip 192 having the cross sectional configurationillustrated in FIG. 7. Filter strip 192 will be used similarly to thetype illustrated in FIG. 1, to form filter element 10, it being notedthat filter strip 180 is embossed on one side only so that both outersurfaces of the filter strip 192 will be smooth.

Reference is not made to FIG. 8, which illustrates apparatus forextruding a generally cylindrical covering over a coiled filter elementof the type described hereinabove. The apparatus of FIG. 8 includes coilfeeding means 200, including a storage rack 210 and a pusher arm 212,which may be operated by a piston 214, which automatically insertscoiled filter strips 216 of the type described hereinabove into anangled extrusion head of a conventional extruder. The extruded productis effectively a continuous extruded tube, having disposed therein atspaced intervals, coiled filter elements 216.

The thus coated and sealed coiled filter elements are then trimmed bytrimming apparatus 218 and are ready for further processing.

FIG. 9A illustrates a coated coiled filter element such as could beproduced by the apparatus of FIG. 8 with coupling ends 220 and 220 whichmay be used for attachment of the filter element to supply and drainconnections.

FIG. 9B shows an alternative arrangment of coated coiled filter elementwith butt ends 260 and 280 which may be attached to connectors 262 and282 intermediate the filter element and a supply or drain connection.

FIG. 9C shows a coated coiled filter element which is essentiallysimilar to that of FIG. 9B, but held inside a housing 290 by sealingrings 292 which are so positioned as to seal the inlet and the outlet.

FIGS. 10, 11 and 12 illustrate a backwashable filter constructed andoperative in accordance with a preferred embodiment of the presentinvention and comprising a housing 230 defining a water inlet 232communicating with a top manifold 234 and a filtered water outlet 236communicating with a bottom manifold 238.

A plurality of coiled filter elements 240 of the type describedhereinabove are located within the housing 230 with a first end thereofin water receiving communication with the inlet top manifold 234 and asecond end thereof in filtered water providing relationship with thebottom manifold 238.

Backflushing is provided by opening the draining valve 242 and by manualrotation of vacuum element 244 by means of handle 246. Vacuum element244 as it scans each coiled filter element at its upstream end, sucks upthe particles accumulated therein.

FIG. 13 illustrates an alternative filter construction including ahousing 250 and a water inlet 252 which communicates with a fluid flowpath 254 formed at the center of a coiled filter element 256. The fluidflow path 254 can conveniently be formed by coiling filter strips arounda hollow tube, using essentially the same production techniques asdescribed hereinabove.

Water exiting from path 254 enters the filter element at an upstream end256 and exits therefrom from a downstream end 258.

FIG. 14 describes a backflushable filter of the type illustrated in FIG.13. Backflushing is provided by opening the draining valve 262 and bymanual rotation of vacuum element 264 by means of handle 266. Vacuumelement 264 scans the filter element at its upstream end and sucks upthe particles accumulated therein.

It will be appreciated by persons skilled in the art that the presentinvention is not limited to what has been particularly shown anddescribed hereinbelow. Rather the scope of the present invention will bedefined only by the claims which follow:

I claim:
 1. A filter element, comprising:at least one filter striphaving first and second lengthwise-extending edges, said at least onefilter strip being rolled in close engagement to form a coil having alongitudinal axis, the first and second edges of said coiled at leastone filter strip forming first and second ends of said coil, one of theends of said coil defining the inlet end of said coil and the inlet edgeof said filter strip during filtering operation, receiving fluid to befiltered, and the other of the ends of said coil defining the outlet endof said coil and the outlet edge of said at least one filter stripduring filtering operation, through which filtered fluid leaves the coilstrip; said at least one filter strip having at least a first and asecond surface, said first surface having a continuous protrusion ofgenerally undulating configuration and said second surface beingsubstantially free of protrusions, such that when said at least onefilter strip is coiled, said first and second surfaces are broughttogether in close engagement and define therebetween upstream anddownstream extending chambers separated by said protrusions, saidupstream extending chambers opening at the inlet end of said coil andsaid downstream extending chambers opening at the outlet end of saidcoil, the ridge of said protrusion on said first surface and the face ofsaid second surface being configured such that when in contact with oneanother, filter pathways of predetermined size are created extendingbetween said upstream and downstream extending chambers for fluid flowfrom the upstream chambers to the downstream chambers and foraccumulation of particles of larger size than said pathways in saidupstream extending chambers during filtering operation.
 2. A filterelement in accordance with claim 1, further including a generallycylindrical sleeve covering the outer perimeter of said coil in closeengagement therewith.
 3. A filter element in accordance with claim 1,wherein said at least one filter strip consists of a single filterstrip, said first surface being one side of said single filter strip andsaid second surface being the other side of said single filter strip. 4.A filter element in accordance with claim 1, wherein said at least onefilter strip consists of two filter strips, both sides of one of saidfilter strips having a continuous protrusion of generally undulatingconfiguration and both sides of the other of said filter strips beingsubstantially free of protrusions, whereby, when coiled, a surface withprotrusions is always in contact with a surface without protrusions,said contacting surfaces being said first and second surfaces of said atleast one filter strip.
 5. A filter element in accordance with claim 1,wherein said second surface has an array of continuouslengthwise-extending grooves therein, said grooves forming said filterpathways when in close engagement with the ridges of the protrusion ofsaid first surface.
 6. A filter element in accordance with claim 1,wherein the ridge of said protrusion of said first surface has aplurality of grooves therein, said grooves forming said filter pathwayswhen said protrusion is in close engagement with said second surface. 7.A filter element in accordance with claim 6, wherein said second surfaceis substantially smooth.
 8. A filter element in accordance with claim 3,wherein said second surface has an array of continuouslengthwise-extending grooves therein, said grooves forming said filterpathways when in close engagement with the ridges of the protrusion ofsaid first surface.
 9. A filter element in accordance with claim 3,wherein the ridge of said protrusion of said first surface has aplurality of grooves therein, said grooves forming said filter pathwayswhen said protrusion is in close engagement with said second surface.10. A filter element in accordance with claim 4, wherein said secondsurface has an array of continuous lengthwise-extending grooves therein,said grooves forming said filter pathways when in close engagement withthe ridges of the protrusion of said first surface.
 11. A filter elementin accordance with claim 4, wherein the ridge of said protrusion of saidfirst surface has a plurality of grooves therein, said grooves formingsaid filter pathways when said protrusion is in close engagement withsaid second surface.
 12. A filter element in accordance with claim 1,wherein said first and second surfaces are bonded together.
 13. A filterelement in accordance with claim 12, wherein said first and secondsurfaces are welded together.
 14. A filter element in accordance withclaim 12, wherein said first and second surfaces are glued together. 15.A filter element, comprising:at least two filter strips, each havingfirst and second lengthwise-extending edges, said at least two filterstrips being coiled in close engagement to form a coil having alongitudinal axis, the first and second edges of said coiled filterstrips forming first and second ends of said coil, one of the ends ofsaid coil defining the inlet end of said coil and the inlet edge of saidfilter strips during filtering operation, receiving fluid to befiltered, and the other of the ends of said coil defining the outlet endof said coil and the outlet edge of said filter strips during filteringoperation, through which filtered fluid leaves the coiled strip; said atleast two filter strips including a first filter strip, formed fromporous material, and a second filter strip, said second filter striphaving first and second surfaces each of said first and second surfaceshaving raised portions defining filter grooves, each said groove beingsurrounded on all lengthwise and axial direction sides by said raisedportions, except for one opening in the axial direction, such that whenthe first and second surfaces of said second filter strip are in closeengagement with a first porous filter strip, said filter grooves formelongated chambers, and wherein the chambers which open at the inletedge of said strip and are defined as upstream chambers and the chamberswhich open at the outlet edge of said strips and are defined asdownstream chambers, said first porous filter strip being disposedadjacent said second filter strip such that when coiled, said firstporous filter strip is disposed between said upstream chambers and saiddownstream chambers to thereby form porous pathways between saidupstream and downstream chambers for fluid flow from the upstreamchambers to the downstream chambers and for accumulation of particles oflarger size than said pathways in said upstream chambers duringfiltering operation.
 16. A filter element in accordance with claim 15,wherein said first surface of said second filter strip contains onlyupstream chambers and said second surface of said second filter stripcontains only downstream chambers, said first porous filter strip beingdisposed between said upstream chambers of the first surface of a secondfilter strip and said downstream chambers of the second surface of asecond filter strip.
 17. A filter element in accordance with claim 16,wherein said upstream chambers are inclined at an angle with respect tosaid downstream chambers such that each said upstream chamber willcommunicate, through said porous filter strip, with a plurality of saiddownstream chambers.
 18. A filter element in accordance with claim 15,further including a generally cylindrical sleeve covering the outerperimeter of said coil in close engagement therewith.
 19. A filterelement in accordance with claim 15, wherein said first and secondfilter strips are bonded together.
 20. A filter element in accordancewith claim 18, wherein said first and second surfaces are weldedtogether.
 21. A filter element in accordance with claim 18, wherein saidfirst and second filter strips are glued together.